In several data transmission systems linearity of a power amplifier limits the achievable maximum transmission power, in particular, when a transmitted signal has a high peak-to-mean ratio. Thus, a signal to be applied to a power amplifier may momentarily show high power or amplitude values, which have to be taken into account in designing the power amplifier. In practice, this means that the amplifier input signal is to be scaled to a lower power or amplitude level for meeting the spectrum requirements of the data transmission system employed. This method, which is known as back-off, provides that the amplified signal is located in an area, where the amplifier transmission function is more linear. However, there is a problem that the back-off lowers the performance of the amplifier and/or the transmitter. On the other hand, the power amplifiers having a wide linear working range, are expensive and their performance is relatively poor.
Methods, by which signal power peaks are clipped, have also been developed. In one prior art clipping method, the power or amplitude values of a signal are given a threshold, and signal sections exceeding said threshold are clipped such that the threshold value is set to be the amplitude or the power and otherwise the signal values are not changed. However, this clipping method has a disadvantage that the frequency spectrum of the signal spreads out, in general, the spectrum spreads outside the assigned frequency band and thus causes interference to other users. The clipping methods generally have a drawback that they can only clip one signal at a time, and therefore they are poorly applicable to multi-carrier systems.